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The speed of light is almost 300 000 km/s.

The photons have a speed along the wave, and the wave have a speed straight forwards.

What is the speed of light? Is it the speed the photons have along the waveline, or is it the speed the wave travels in a straight line?

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This is absolutely fundamental: small enough particles or short (wavelength) enough waves can be described either as particle or as wave, but never as a mixture of both! This antinomy is the most basic thing in quantum mechanics. – Georg Dec 5 '11 at 15:25
Know, we were just introduced to the subject at school. But our teacher didn't know the answer, so I asked it here... – Friend of Kim Dec 5 '11 at 15:38
No problem, now You know! As an ointment to Your wounds: there are members with a physics degree here who slip on this point frequently. – Georg Dec 5 '11 at 15:45
Thanks! It's really interesting this stuff, looking forward to learn more! – Friend of Kim Dec 5 '11 at 15:53
The photons don't go forward in time--- there is no causal particle picture in relativity. – Ron Maimon Aug 1 '12 at 8:35
up vote 3 down vote accepted

Its both, if you are talking about the vacuum. But you certainly are confused by the wave/particle thing in quantum mechanics.

It's not that there's a wave and photons travel on it. The reality is that light is something that can be precisely modeled by the equations of quantum mechanics. However, its properties are not easy to understand, and sometimes it's easier to think of light as a wave (for example, when you think about how your radio works, or how a laser can make patterns when you put a hair in its path) and sometimes it's easier to think of it as a particle (for example, when talking about atomic emissions, or detection with a photomultiplier). Both of these models are easy to understand, but neither of them are correct.

However, it doesn't matter if you think of a wave or a photon or the complete quantum model, in vacuum the speed of light is $c=299792.458\,\mathrm{km}/\mathrm{s}$.

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